As regards connection between adherends, for example when various electric devices are produced by connecting a semiconductor chip on a substrate or by connecting a tape carrier package (hereinafter abbreviated to TCP) and a liquid crystal display (hereinafter abbreviated to LCD), it is often executed with an adhesive containing conductive particles.
FIG. 9 shows a schematic cross-sectional view of the main parts of an electric device 101 constructed by bonding an LCD 111 and a TCP 115 with an adhesive 125 containing conductive particles 130.
The TCP 115 is composed of a base film 116, and metal wirings 117 formed in such a manner that they are adhered to the surface of this base film 116.
The LCD 111 has a substrate 112 formed of a glass substrate, and electrodes 113 disposed on the surface of this substrate 112 in such a manner that they face the metal wirings 117 of the TCP 115.
The conductive particles 130 in the adhesive 125 are sandwiched between the electrodes 113 and the metal wirings 117; the electrodes 113 and metal wirings 117 corresponding with each other are electrically connected with those conductive particles 130, and concurrently the LCD 111 and the TCP 115 are mechanically joined with the adhesive 125.
In this manner, the LCD 111 and the TCP 115 are electrically and mechanically connected.
Hereupon, if the electrodes 113 of the LCD 111 are made of a metal that easily oxidizes such as aluminum or chromium, oxide thin films are formed on the surfaces of the electrodes 113 with the natural oxidation of the metal. In this case, if oxide coatings are formed on the surfaces of the electrodes 113, only the conductive particles 130 being sandwiched between the electrodes 113 and the metal wirings 117 renders electrical conduction unreliable. However, if hard particles such as metal particles are used as the conductive particles 130, the reliability of the conductive portion of the electric device 101 increases; because those conductive particles 130 penetrate the oxide coatings on the surfaces of the electrodes 113 in a heating and pressing process, the conductive particles 130 and the electrodes 113 directly touch each other.
However, if the electrodes 113 of the LCD 111, which is an adherend, are soft or the pattern of the electrodes 113 is minute, when hard conductive particles 130 of the above-mentioned kind are used, the substrate 112 and the metal wirings 117 may deform or break in the heating and pressing process.
In addition, metal particles are low in coefficient of linear expansion and modulus of elasticity in comparison with a binder of an adhesive, so that when a binder reacts (recovers from deformation) after finishing the heating and pressing, the contact between the conductive particles 130 and the metal wirings 117 may break.
To connect such adherends with each other, a conductive particle 140 in which a conductive thin film 142 is adhered to the surface of resin particle 141, whose schematic cross-sectional view is shown in FIG. 10, is used.
The resin particle 141 is soft in comparison with metal particles and has approximately the same coefficient of linear expansion as that if a binder in an adhesive.
Therefore, if such conductive particle 140 is used, a soft adherend does not break and the resin particle 141 recovers from deformation along with a binder in an adhesive, so that the contact between the conductive particle 140 and a metal wiring is maintained.
However, since this conductive particle 140 is soft in comparison with conductive particles formed of metal particles, it is possible that if adherends are hard, the resin particle 141 may deform excessively by pressure, a crack may occur in the conductive thin film 142, and so conductive resistance at connecting portions may increase.
Also, if, for example, an oxide coating is formed on an electrode surface with natural oxidation, there may be the case in which the conductive particle 140 can not penetrate the oxide coating, thereby lowering the conductive reliability of the electric device 101.
Thus, it is necessary to change the kind of conductive particles depending on the kind of an adherend, so that it has been difficult to use conductive particles of the same kind for connection between various kinds of adherend.